In November last year, the Serious Fraud Office (SFO) set up a prayer room, giving staff space for “quiet reflection” in between fighting white-collar crime.

Perhaps Robert Wardle, the director of the SFO, sought divine intervention within the haven before the investigation into alleged corruption by BAE Systems officials in the £43 billion al-Yamamah oil-for-arms deal with Saudi Arabia was halted in December.

Despite Mr Wardle’s many protestations that stopping the inquiry was his decision, made independently – he even says as much in this year’s annual report – there is something of the fall guy about him, a man clearly under some conflict about what he did.

Halting the BAE investigation was obviously an agonising decision.

The aftermath has engulfed the SFO, leaving a question mark over the organisation’s reputation, despite the oft-repeated justification that calling off the inquiry was necessary to protect national security.

There is the question whether Mr Wardle bowed to political pressure from Tony Blair and Lord Goldsmith, the former Attorney-General, to drop the case lest Britain lose out on a £20 billion contract to supply Eurofighter aircraft to Saudi Arabia.

Speaking to The Times, an amiable but emphatic Mr Wardle declared: “You say ‘when Tony Blair stopped the investigation’. Well, he didn’t, I did. But I hope people realise we were in a very awkward position, we had to make a very tough decision.

“With hindsight, I very much doubt I could see a way of having avoided it.”

That is part of Mr Wardle’s problem. He chose to drop the case on security concerns, a decision based on information that he cannot conclusively prove to be true – information that was co-ordinated by the Cabinet Office.

“It is my job to make decisions whether to investigate or to prosecute,” Mr Wardle said. “Those are independent of the Government, certainly independent of party political issues, but I cannot ignore the wide public interest.”

He did admit that he stopped the investigation on “information I am unable to test” and added: “I cannot necessarily accept whether it is credible or not. I took the best information, the best advice I could get in circumstances.”

Mr Wardle is an approachable man, so much so that you want to believe his reason for dropping the investigation almost as much as he seems to want to believe it himself.

Yet when questioned about the impact of the decision on the agency, he is clearly uncomfortable about the ramifications. “I don’t think anyone was very happy about it, put it that way,” he said.

“On the other hand, I think that our people are professional, they understood why the decision had to be made . . . but they were disappointed, certainly.”

The SFO faces huge embarrassment if the Department of Justice (DoJ) in the United States, which recently launched its own investigation into the al-Yamamah deal, decides to go ahead with a prosecution.

Mr Wardle says that American legislation allows a more modern approach to dealing with corruption than Britain’s own, rather archaic laws . . . “but, yes, it would not make us look good. I fully accept that but that is some way down the line.”

On top of this is the fact that the SFO is still investigating six other allegations of corruption by BAE officials in South Africa, Romania, Chile, the Czech Republic, Tanzania and Qatar.

There could be pressure to secure convictions in these cases to mitigate for the decision to halt the Saudi Arabia inquiry.

Mr Wardle is reluctant to give a timetable for concluding the six outstanding investigations. Heavy hints that he may leave the SFO next April after five years at the helm mean that he could be seen as something of a lame duck in this final year of his tenure – unless, of course, the thought of leaving a legacy marred by the Saudi Arabia decision spurs him on to secure convictions in the six other cases.

“I am quite satisfied that I and the lawyers and the investigators are not pursuing this as a witch hunt or anything else like that,” Mr Wardle said. “They’re not.

“They are saying: ‘Let’s try to find out the facts as far as we can and see whether these decisions can be proved. If not, then let’s get out of it. For BAE’s sake as much as ours, we need to resolve this as quickly as possible’.”

In this last year of Mr Wardle’s tenure, BAE will be a priority, but so, too, is the future of the SFO, which is being examined as part of a review commissioned by the director and by Lord Goldsmith, who has since been replaced by Baroness Scotland of Asthal.

Mr Wardle is looking forward to the findings of the review and whether the architect of the report, Jessica de Grazia, finds ways of speeding up the often cumbersome process of pushing a fraud allegation all the way through to a prosecution and possibly a conviction.

Of the 11 trials that have been completed in the latest financial year, involving 21 defendants, 15 were convicted – a success rate of 71 per cent.

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